Hi there, really cool team, i love Zappo, even if i often prefer Sub+Roost version to stall better the oppo, the 3attacker is a great alternative thanks his expanded coverage that make it more dangerous. The team in general seems pretty good, but i ve some advice to give you, especially for a serious weakness, so let s start with the rate!
In a metagame that is full of Fight spam, you have 3 resistors, Zappo, Lando-t (helped by his trait) and Starmie, but these 3 pokemon and your team accordingly have a big trouble, his name is Toxicroak. Toxicroak can without any problem Setup on Ferrothorn, Zapdos and especially on Tyranitar (that has no way to hit him decently although has Choice Band set) and destroy all your team since is pretty slow (him outspeeds 4/6 and has access to Sucker Punch, that s one of the best Priority moves) without finding any resistance, only Stoutlant could be not Hokoed by him, but only if you have not Entry Hazard in your field. Here some calc.
252Atk Life Orb +2 Toxicroak (+Atk) Sucker Punch vs 0HP/4Def Stoutland (Neutral): 75% - 88% (235 - 276 HP). Guaranteed 2HKO.
252Atk Life Orb Toxicroak (+Atk) Ice Punch vs 248HP/0Def Lightningrod Zapdos (Neutral): 61% - 71% (234 - 274 HP). Guaranteed 2HKO.
252Atk Life Orb Toxicroak (+Atk) Cross Chop vs 252HP/88Def Ferrothorn (Neutral): 85% - 100% (300 - 354 HP). Guaranteed 2HKO. 3% chance to OHKO.
252Atk Life Orb Toxicroak (+Atk) Ice Punch vs 252HP/212Def Landorus Therian (Neutral): 93% - 110% (356 - 424 HP). Guaranteed 2HKO. 61% chance to OHKO.
As you can see, Toxicroak give you much problems even if doesn t boost, has even the possibility to Hoko Zapdos without SD up (Stealth Rock+ Sand Damage), and Ferrothorn has not the certainty to use an eventual Thunder Wave to stop eventually after with Landorus. So My suggestion is to use a different Evs spread on Landorus-T. Originally i wanted to replace Skarmory in place of Ferrothorn, same work, similar utility, but Skarmory is only a check and you have in your home the answer for that threat. I suggest you to run with one of 200HP/102Def/208Spd Impish Nature
; this Evs spread allows you to outspeed Adamant Toxicroak and give you the possibility to Hoko him thanks his Stab Earthquake.
Last thing, you should give Gyro Ball instead of Power Whip and Protect over Thunder Wave
on Ferrothorn, the reason is simple, Gyroball help you to don't give setup to pokemon such as CMLatias that in this way could give nuisance to Tyranitar and hit harder Dragon Pokemon in general while Protect is pretty useful to scout the move to an eventual choicer, in this case Bandkion, that with the loss of some investiment on the Def of Landorus-T could be dangerous, in this way you always have the more safe switch in, especially useful in this kind of team.
As you can see, you have not more to change, only some fix, hope i heped and gl with the team.
Landorus-T (M) @ Leftovers
EVs: 200 HP / 100 Def / 208 Spd
Impish Nature (+Def, -SAtk)
- Stone Edge
- Stealth Rock
Ferrothorn (M) @ Leftovers
Trait: Iron Barbs
EVs: 252 HP / 88 Def / 168 SDef
Sassy Nature (+SDef, -Spd)
- Leech Seed
- Gyro Ball